The son of Kofi Annan, the UN secretary-general, tried several times to trade on his father's reputation, a damaging report into the UN oil-for-food programme in Iraq will reveal this week.

However, sources who have seen the 1,000-page study said there would be no new 'smoking-gun' revelations or accusations of impropriety against the UN leader.

Instead, it will show how Kojo Annan, 31, tried to take advantage of his family connections. One example concerns Kojo's attempt to get a discount on a car purchase in Ghana.

However the long-awaited report by the independent commission set up to investigate the scandal-ridden oil-for-food programme will criticise the UN leader for a series of management failures.

The inquiry, set up by Annan and headed by former US Federal Reserve chairman Paul Volcker, will allege a culture of mismanagement, lack of oversight and incompetence throughout the body.

The secretary-general and his Security Council committee, which ultimate controlled the scheme, are among those under fire.

Volcker investigated allegations concerning Kofi Annan and his dealings with a Swiss company, Cotecna, which paid his son as an adviser and won a contract in the oil-for-food programme

Although the report, to be published on Wednesday, clears the UN chief of improper behaviour over Cotecna, the broad criticism over the handling of the world's biggest humanitarian scheme will raise fresh questions over his future.

To make matters worse, its publication will be on the eve of a world summit at the UN's headquarters in New York to mark its 60th anniversary. Annan tried to pre-empt the study's impact by unveiling reform proposals of his own as the scale of the oil-for-food scandal became clear. But critics, particularly in Washington, claim they do not go far enough.

The United States' new ambassador to the UN, John Bolton, has signalled his determination to scupper Annan's reforms by objecting to proposed UN commitments on aid to developing countries, combating global warming and nuclear disarmament.

Running to more than 1,000 pages and based on a study of more than 11 million documents and emails, Volcker's report is the result of a year's investigation by a three-man committee.

A source familiar with the committee's findings told The Observer that, while it would deliver the 'final word' on the political side of the oil-for-food failings, there would be further bad news for the UN next month, in a separate report on the 4,500 private companies 'involved either in purchasing oil or supplying goods'.

'Adverse findings' notices had already gone out to 'up to 2,500 corporations around the world' that the committee suspects of violating Iraq sanctions or otherwise behaving improperly, the source said.

Notices had also gone out to 'about a dozen individuals', including Kofi Annan, whom the committee intended to criticise. The secretary-general was told the report would include 'additional evidence and conclusions' about his role in the programme.

A senior UN source confirmed that the report had rejected the most serious accusation - that he attempted to influence business for his son. 'Essentially there is more evidence that Kojo traded on his father's name. This is ultimately a report about the fact that the management of the UN is unmodernised,' he said.

After an interim report last March, the secretary-general claimed he had 'been exonerated' by Volcker, who was unable to prove that he knew Cotecna had bid for the contract before it was awarded. However, in June Cotecna released an emailed letter suggesting that its former executives and Annan did discuss the contract ahead of its being awarded. Even so, Volcker will clear Annan of improper dealings.

Instead, top UN officials are braced for a 'detailed and comprehensive' indictment of the entire programme. 'I'm sure there are going to be some nasty stories of venal, stupid behaviour - maybe not of corruption in the billions, but a lot of bad stuff,' one said.

In a sign of a dramatic change in tone, the official said all the UN's top figures recognised that the oil-for-food scheme went badly wrong 'from the start'.

The secretary-general's office, he said, knew that 'we did lots of very bad things'. But the scandal had uncovered a larger, systemic UN problem which Annan hoped would help bring consensus on proposals for reform.

'This was an organisation set up to do diplomacy, but, as oil-for-food epitomised, got into managing and spending millions and millions of dollars without being equipped to do so properly,' the source close to Annan said.

The programme - set up in 1995 to provide humanitarian supplies to Iraq during sanction - was subverted by Saddam Hussein who took bribes from firms involved.